When comparing Selenium vs unobtainium, the Slant community recommends Selenium for most people. In the question“What are the best test automation tools for web apps?”Selenium is ranked 1st while unobtainium is ranked 10th. The most important reason people chose Selenium is:

The WebDriver protocol is standardized by the World Wide Web Consortium which makes it easy for third-parties to get involved and contribute to Selenium.
WebDriver has been the foundation of many additional automation projects besides core selenium and has become the de-facto standard for UI automation.

Pros

Pro

Uses an approved WC3 standard - WebDriver

The WebDriver protocol is standardized by the World Wide Web Consortium which makes it easy for third-parties to get involved and contribute to Selenium.WebDriver has been the foundation of many additional automation projects besides core selenium and has become the de-facto standard for UI automation.

Pro

Integrates with any CI tool

Selenium, with its ability to interact with different testing frameworks, like NUnit or xUnit, makes it easy to get Selenium working with practically any Continuous Integration services.

Pro

Actively supported

The open source community behind Selenium has a very large & engaged developer base. This ensures a stable support channel for the tool. In addition, various companies also provide support for Selenium. This active and multi-channel support provides a much more lucrative option for developers looking to implement Selenium in their workflow.

Pro

Support for many languages

Selenium supports a variety of languages including Java, Python, PHP, C#, Ruby and JavaScript ensuring that the tool is easily accessible to a wide variety of developers.

Pro

Cross-platform

Selenium is based on Java and can be run on Windows, Mac, Linux, Unix, etc.

Pro

Cross-browser

Supports many browsers and a solid platform for adding future browsers to selenium (WebDriver)

Pro

Integrates well with existing testing frameworks

Pro

You can use the same IDE you use for coding to debug

Pro

Ability to imitate a real user using the application

Testing is analogous to a human being using the web application which is not possible with a solution which runs headless and claims to run faster than Selenium.

Pro

Use the very minimum amount of code required to run

Selenium tries to inject into the page only the bare minimum of code needed to run the tests.

Pro

Easy to set preconditions for the tests

Pro

Extensible

Custom drivers for e.g. API testing or static HTML testing exist and are easily built. Driver modules allow you to extend the main driver (e.g. Selenium or Appium) with ease.